This invention relates to machines for producing ropes and cables, and is more particularly directed to machines of the type in which a rotating tube carries a number of cradles, each of which remains stationary while the tube rotates about it, and each of which feeds a strand to form the rope or cable. In systems of this type several tube sections can be joined end to end for producing a rope or cable of a larger number of strands.
The invention is more specifically directed to support arrangements which flexibly support the tube sections and to coupling arrangement which can accommodate angular, axial and parallel misalignment when two or more sections are joined together in a cable stranding machine. The use of a flexible support is also valuable in a smaller machine with only one tube since it isolates vibration and protects the encircling bearing from abnormal loads which can occur with misalignment.
Tubular stranding machines, also known as Larmuth type machines, have been in use for many years and are well known. In these machines, the strander tube is supported by bearings or rollers and is rotated under power about its longitudinal axis. Within the tube, spools of single strand wire or fiber cord are rotatably mounted in cradles and the cradles in turn are supported by bearings at each end, the bearings being coaxial with the tube axis. The cradles are weighted at the bottom and do no rotate with the tube, but remain stationary. Normally one spool of wire or cord outside the tube feeds one strand into it, and the tube is built of tube sections each of which typically contains six cradles. Tubular stranding machines are commonly built with one, two or three sections, although there can be more when required. Sections are joined end to end when two or more are used. Cable constructions are most commonly seven strand, nineteen strand, and thirty-seven strand although not limited to these.
The strander tube typically rotates at speeds in excess of 2000 rpm, so it is imperative that the spools remain locked in their cradles. If either the cradle or the spool should shake free and contact the inside of the tube, serious damage to the machine would result.
In multiple section tubular stranding machines, it is impractical to interconnect tube sections with solid connectors so that the entire tube constitutes a rigid body over its entire length. Rigid couplings would require extremely careful alignment in order to avoid vibrating, abnormal bearing loads and fatigue failure. Flexible couplings are therefore preferred. Flexible couplings typically have equally spaced axial pins near the outer diameter of one tube engaging hole in the adjoining tube. These couplings are capable of compensating for angular misalignment, but not parallel misalignment or offset.
Stranding machines are typically forty-five feet long, and conventional stranding machines must be supported from the floor at close intervals and carefully aligned to assure parallel alignment between sections. These precautions are required to reduce transfer of vibration between sections and to keep bearing loads normal.
One previously proposed coupling system is described in U.S. Pat. No. 3,456,433, of July 22, 1969. Here, the tube sections are supported at each end by ball bearings, and the ends of the tube are of reduced diameter to reduce the bearing size. A tubular elastic member connects the outer surfaces of the reduced-diameter ends of the tube sections. However, the strands that exit one tube section must cross each other in precise paths in the reduced-diameter ends, and any parallel misalignment would disturb the passage of strands through them. Consequently, only angular misalignment can be tolerated. Although it has been proposed, e.g. in U.S. Pat. No. 3,693,337, to use elastic or resilient bearings supported on cushions for individual tubular sections that are disposed between cradles, no one has previously suggested that a flexible elastic member should be used to a bearing for a multiple spindle tube from a frame.
Another tubular rope stranding machine, proposed in U.S. Pat. No. 2,416,126, employs spiders at each end of the tube sections, and the spiders are joined by a universal joint, which can be rigid metal or stiff fiber. While this does permit some angular misalignment, it does not allow for axial displacement or offset of the tube sections relative to one another.